Method for drying sawn wood goods in drying kilns



United States Patent 3,336,680 METHOD FOR DRYING SAWN WOOD GOODS INDRYING KILNS Gunnar Lennart Ahlstedt, Alfredshem, Sweden, assignor to M0Och Domsjo Aktiebolag, Ornskaldsvig, Sweden, a corporation of Sweden NoDrawing. Filed July 12, 1965, Ser. No. 471,464 Claims priority,application Sweden, July 17, 1964, 8,751/ 64 3 Claims. (CI. 34-22) Thisinvention relates to a method for drying sawn wood goods.

In the manufacture of wood goods until some decades ago the goods wereusually dried in open timber yards. For reducing the capital tied up inthe timber yards and to accelerate the turnover rate, the wood goods arenow to a large extent subjected to artificial drying. This dryingusually is carried out in drying chambers or drying channels throughwhich preheated air is directed. The air passing through said channelshas as it object both to transport the heat required for drying the woodgoods and to evacuate the water given off during the drying process. Thedrying capacity of artificial drying sheds is in many cases limited bythe fact, that the timber assortment and the drying periods cannotalways be adjusted to the volume of the drying shed available or to thecalorie amount produced by the generation unit in the boiler house orwhich the air is capable to feed to the wood goods. It is well knownthat considerable differences in drying time are obtained when equalamounts with respect to volume of different wood species :are beingdried, such as, for example, goods of pine and spruce. As a resultthereof, an artificial drying plant employed for the drying of, forexample, pine goods can be .utilized to 100 percent and in certain casesprove to be undersized in relation to the manufacturing and handlingcapacity in general for this material, while the drying plant isoversized for another wood species such as, for example, spruce goodswhich are substantially easier and quicker to dry and require smallerdried volumes.

Normally, during a certain period of the year only goods of one woodspecies are manufactured, for example of pine, and during another periodof the year goods of another wood species, for example spruce. Thus, thecapacity of the sawing lines is not fully utilized when sawing one ofthe said wood species, due to the too low capacity of the artificialdrying shed, While during the time needed for sawing the other woodspecies the capacity of the drying shed is not fully utilized in spiteof fully utilized sawing capacity.

The present invention eliminates the aforesaid disadvantages.

The method according to the invention adapted for drying sawn wood goodsin dry-kilns is characterized in that wood species of a shorter dryingtime are dried in the dry-kiln at the same time as wood species of alonger drying time. The term dry-kiln in this connection is to beunderstood as a single so-called drying channel as well as a pluralityof drying channels assembled to a drying unit.

The method is carried out such, that the two wood species are fed intothe drying plant in such proportions that the capacity of the drieravailable is fully utilized. In cases when the drying unit comprises aplurality of drying channels, certain of the channels may be reservedfor the one or the other wood species, but it is, of course, alsopossible to mix the diflerent wood species in the same drying channel inthe proportions according to their drying time, as appears from theexamples.

The application of the invention is illustrated in the examples asfollows.

3,336,680 Patented Aug. 22, 1967 ice Example I The production capacityof a sawmill for sawing pine wood was at full operation of the sawinglines (frame saw lines) about 27 timber packages per 24 hours (1 timberpackage corresponds to about 3 standards). The

dnying unit of the sawmill comprised 8 drying channels each holding l5packages, i.e. a total of 120 packages. At continuous operation and at adrying time of about 5 days for pine timber the drying unit could becharged with about 24 packages per day. At full operation of the framesaw lines for pine timber there Was, thus, a surplus of 3 packages aday. When sawing spruce timber in the frame saw lines, at full operationthe same amount as in pine sawing could be delivered to the drying unit.Due to the shorter drying time of the spruce timber, about 3-4 days, thedrying unit could be charged continuously with about 27 packages ofspruce timber per day, which involved that for every cycle only 6 of the8 drying channels had to be utilized.

When the drying unit according to the invention was charged with spruceand pine, the pine timber was supplied from two frame saw lines to 6 ofthe channels of the drying unit and the spruce timber from one frame sawline to the remaining two channels in the drying unit, thereby utilizingthe full capacity of the drying unit, i.e. 27 packages per day. Thismeans in practice that for a sawmill which, for example, for 8 months ofthe year sawed pine timber and for the remaining 4 months spruce timber,a capacity of 8 8=64 channel months of pine and 4 6=24 channel months ofspruce were obtained, i.e. a total of 88 channel months by applying theconventional method. By sawing according to the invention, however, whenthe entire drying unit was utilized, a capacity of 8 l2=96 channelmonths was obtained.

Example 2 ing unit was achieved at the same time as full employment forthe personnel could be provided.

With respect to sawing, the invention, in other Words, implies the ideaof sawing different kinds of raw goods in one or several lines in such amanner, that the quantities of sawn goods obtained complete each otherwhen being fed to the drying plant, so that for promoting the productionthe artificial timber shed is well utilized during the entire productionyear.

When applying the invention, the different types of raw goods may alsobe sawn in different Ways relative one another-this applies especiallyto so-called sideboards for which, for example, spruce goods are giventhe thickness A;" and /s" respectively and pine goods the thicknesses 1"and %1" respectively. In this Way, the said good can be measuredautomatically and sorted with respect to their dimension even when theyare mixed and transported at relatively high velocities. Thus, an easysorting into different types of timber is obtained which can be utilizedin connection with the charging of the drying plant. The centre yieldwhich substantially is much coarser, is found in a smaller number andcan easily be divided as to wood species, because it usually istransported on separate conveyors, at least one for every sawing line.

goods may also be marked in difierent ways, which marks may be sensed,for example, by photoelectric cells controlling the sorting.

The proposed method which, of course, is adaptable also to any woodspecies other than spruce and pine eliminates the disadvantagesmentioned above with respect to the utilization degree of the artificialdrier and follows a more uniform employment of the personnel.

What I claim is:

1. A method of utilizing the full drying capacity of a kiln for dryingsawed wood products by drying sawed products of different varieties andhaving diiferent drying times in the kiln at the same time, whichcomprises selecting at least two varieties of sawed products, of whichat least one of the varieties has a faster drying time, and introducingsuch wood products into the kiln in an amount sufficient tosubstantially fill the kiln, and in volume proportions to one anotherrelated to the drying time of each variety, the capacity of the kiln,and the saw production capacity, continuously drying the wood productsin the kiln, and removing the dried sawed wood products of each varietyfrom the kiln when dried, so that each variety is present in the kilnfor the least possible drying time, the faster drying variety beingpresent for the shorter time, and replacing the dried wood products asthey are removed with more sawed wood products, in an amount sufficientalways to keep the kiln substantially filled, and at maximum capacityfor the saw production of each variety.

2. A method in accordance with claim 1 wherein at least one of thevarieties of wood products is identified according to drying time.

3. A method in accordance with claim 1 wherein the wood productscomprise a mixture of pine and spruce.

References Cited UNITED STATES PATENTS 2,288,154 6/1942 Cobb 3426KENNETH W. SPRAGUE, Primary Examiner.

1. A METHOD OF UTILIZING THE FULL DRYING CAPACITY OF A KILN FOR DRYINGSAWED WOOD PRODUCTS BY DRYING SAWED PRODUCTS OF DIFFERENT VARIETIES ANDHAVING DIFFERENT DRYING TIMES IN THE KILN AT THE SAME TIME, WHICHCOMPRISES SELECTING AT LEAST TWO VARIETIES OF SAWED PRODUCTS, OF WHICHAT LEAST ONE OF THE VARIETIES HAS A FASTER DRYING TIME, AND INTRODUCINGSUCH WOOD PRODUCTS INTO THE KILN IN AN AMOUNT SUFFICIENT TOSUBSTANTIALLY FILL THE KILN, AND IN VOLUME PROPORTIONS TO ONE ANOTHERRELATED TO THE DRYING TIME OF EACH VARIETY, THE CAPACITY OF THE KILN,AND THE SAW PRODUCTION CAPACITY, CONTINUOUSLY DRYING THE WOOD PRODUCTSIN THE KILN, AND REMOVING THE DRIED SAWED WOOD PRODUCTS OF EACH VARIETYFROM THE KILN WHEN DRIED, SO THAT EACH VARIETY IS PRESENT IN THE KILNFOR THE LEAST POSSIBLE DRYING TIME, THE FASTER DRYING VARIETY BEINGPRESENT FOR THE SHORTER TIME, AND REPLACING THE DRIED WOOD PRODUCTS ASTHEY ARE REMOVED WITH MORE SAWED WOOD PRODUCTS, IN AN AMOUNT SUFFICIENTALWAYS TO KEEP THE KILN SUBSTANTIALLY FILLED, AND AT MAXIMUM CAPACITYFOR THE SAW PRODUCTION OF EACH VARIETY.